Process to concentrate sulphite-lye or other liquors by freezing



May 3, 1966 E. MAN 3,248,890

PROCESS TO CONCENTRATE SULPHITE-LYE OR OTHER LIQUORS BY FREEZING Filed March 6, 1963 6 Sheets-Sheet 1 ER//f A//A/v May 3, 1966 E. MAN 3,248,890

PROCESS TO GONCENTRATE SULPHITE-LYE OR OTHER LIQUORS BY FREEZING Filed March 6, 1965 6 Sheets-Sheet 2 Fi g .2 afm/ua snag mob/mn ER//f MAN /NvE/VTOR, BY M55 A TTORNEY.

May 3, 1966 E. MAN

PRocEss To coNcENTRATE sULPHITE-LYE OR OTHER LIQUORS BY FREEZING Filed March 6, 1963 6 Sheets-Sheet 5 clflvlllvllrnar v :Illia A T TURA/EY,

May 3, 1966 E. OMAN 3,248,890

PROCESS To CONCENTRATE SULPHITE-LYE OR OTHER LIQUORS BY FREEZING 6 Sheets-Sheet 4 Filed March 6, 1963 .ER/K MA/v /Nve/vTa/e. BY Wg@ ATTORNEK May 3, 1966 E. MAN PROCESS TO GONCENTRATE SULPHITE-LYE OR OTHER LIQUORS BY FREEZING 6 Sheets-Sheet 5 Filed March 6, 1963 o llllllllalllllllllallll 'Il' Ill"- 'Il' Ee/K MAN l /NVEA/ToR.

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May 3, 1966 E. MAN

PRocEss To ooNcENTRATE SULPHITE-LYE OR OTHER LIQUORS BY FREEZING 6 Sheets-Sheet 6 Filed March 6, 1963 ATTURNEY.

United States Patent O 3 248,890 PROCESS T CGNCNTRATE SULPHITE-LYE "OR OTHER LIQUORS BY FREEZING Erik 01mm, Djursholrnsvagcn 40, Stocirsund, Sweden Filed Mar. 6, 1963, Ser. No. 263,322 8 Claims. (Cl. 62-58) In concentrating sulphite waste lye by freezing-out the Water (freezing concentration), it is an important desideratum to obtain the ice in the form of large crystals (ice-needles), because otherwise the-separation of the lye from the ice-crystals will be very difficult.

3,248,830 Patented May 3, 1966 application owing to the large quantities of liquor to be treated.

The freezing-point of the sulphite lye declines at rising concentration (contents of dry-substance) but above the liquor there prevails a modest water vapour pressure, which is reduced with declining freezing-point. The following Table -I shows, for `different percent by weight drysubstance inthe lye, the freezing-point, the pressure of the water vapour above pure ice (snow) at this tem- 10 perature, and the freezing-point reduction -corrected for dissolved substances, that is to say, the water vapour pres- Further, sure above the sulphite lye at 1ts freezing-point.

Table I The concentration of the sulphite lye in percent by weight 10 15 20 25 30 35 40 45 The freezing point C.) of the sulphte lye at these concentrations 0.58 0.93 1.31 1.77 2.31 3.00 3.80 4.80 Water vapour pressure nnn. Hg above ice at these temperatures 4.37 4.24 4.11 3.95 3:78 3.57 3.33 3.06 This pressure corrected for 'dissolved A substance 4.35 4.22 4.07 3.91 3.72 3.50 3.23 2.94

it is a dominating desideratum to ycontinue the freezing concentration to as high lye-concentration as possible, in spite of fact that the viscosity of the lye strongly increases on increasing concentration. The difficulties in this technical performance are ea-sily realized, when it is considered that the lye quantities, which are to be treated in modern sulphite cellulose mills, are of the magnitude 30 to 50 m.3 .per hour.

The present invention relates to a process and an apparatus, whereby the aforesaid difficulties are eliminated at relatively low cost.

The sulphite lye (such as it comes from the sulphite mill) and has a concentration of approximately 12 to 14 up to approximately 45 percent by weight. Hereby, however, the viscosity increases 4from 1 to 35, but, with increased viscosity it will be increasingly more difficult to cause the ice-crystals to grow to the required size so to render easy and relatively complete separation of lye from ice-crystals (which can take place in different ways) possible.

The main object of the present invention is to eliminate these disadvantages. According to the invention the sulphite lye-after having been cooled to approximately 0 C.-s frozen in a first step by partially evaporating the water-contents of the lye under the action of vacuum, approximately at the freezing-point of the lye, and the lye thus concentrated is cooled in a second step to a lower temperature than said freezing-point, preferably approxi- 50 091:1 .0 kilognamcalories.

The sulphite lye having a predetermined concentration and cooled down to 0 C. is subjected to the above pressures Iby evacuation, which causes the water-vapour to evaporate from the lye. Hereby a certain quantityl of heat Will be consumed for the vaporization so that lye will be cooled from 0 C. to its freezing-point and moreover the quantity of ice corresponding to the remaining calories will be frozen. Evacuation-pumps are available,

which work very well at these low water-Vapour pressures so that a large quantity of ice can be produced easily.

In the following table II there has been calculated the quantity of ice frozen-out when 2%, 4%, 5%, 6%, 7% percent lby weight and it can be concentrated by freezing and 8%, respectively, of the total weight of the lye evaporates as water-vapour for a certain lye-concentration (14.0% dry-substance, that is to say 149 g. dry-substance per 1.00 kg., a Icertain freezing point 0.85, specific weight 1.057, and specific heat 0.91). For 2% evaporated liquid the calculation will be the following lstarting from the original quantity 1.00 kg. sulphite lye.

The freezing-point of the lye initially is 0.85 C. but declines in the course of the evaporation and is towards the end 1.14" C., which gives an approximate value of 1.1" C. (for the entire time). 2% give 0.020 kg. Water-vapour, which consume 0.020 \600=12.0 kilo- I-gram'calories. In order to reduce the temperature of the lye yfrom 0 to 1.1 C. there aire consumed 1.00 v 1.1

Thus for the ice-production there remain 12.0 1.0=11.0 kilogramcalories.

Table Il [Per 1.00 kg. lye] The remaining lye Kg. evap- Kg. water Kcal. for orated evaporated ice ior- Kg. ice liquid Percent Freezing- Viscosity mation etc. -I- ice Kg. dry subpoint in absolute stance C.) value at +15 C.

mately at atmospheric pressure. `The invention also relates to an apparatus for carrying out the method.

In this manner the largest possible ice crystal size can be achieved in the entire concentration range. Preferably, both steps are divided into t-Wo or a plurality of additional steps, which can be necessary in the technical Throughout the specication temperatures are given in degrees centigrade C.).

Viscosity tests at the freezing-points show that this viscosity is approximately 2.5 times as great as at +15 C.

For 25.4 percent by weight (freezing-point 1.8) the viscosity will thus be 2.5 4.57=11.4.

For 29.6 percent by weight (freezing-point -2.25 the viscosity will be 2.5 X685: 17.1.

For 35.2 percent by weight (freezing-point -3.05) the viscosity will be 2.5 l3.4=33.5. v

At approximately 30 percent by weight dry-substance the viscosity of the sulphite lye (at its freezing-point) will thus increase highly with increased concentration. Thus, 30 percent by weight will be the limit value between the two steps.

One embodiment of an apparatus for carrying out the invention is shown schematically on the accompanying drawings.

FIG. 1 shows the apparatus for carrying out the iirst step,

FIG. 2 shows the apparatus for carrying out the second step,

FIG. 3 shows a part of this apparatus, partly in section,

FIG. 4 shows part of the apparatus on a larger scale in longitudinal section,

FIG. 5 shows a driving mechanism for the apparatus according to FIG. 4, and

FIGS. 6 and 7 illustrate two different alternative embodiments of part of the apparatus according to FIG. 1.

The lye or liquor to be concentrated enters the rst stage of the plant through a duct 6, is cooled approximately to C. in a cooler 7 with ice land Water, and subsequently conveyed through a duct 8 to a mixer 9 having agitators. From mixer 9 the lye is fed through a suction-duct 12 having a control-valve 11 into an evaporation vessel 1, having a Vapour outlet 2 at its upper end. Said outlet communicates with a compressor 3 for the water-vapour, whereby, for instance, its pressure is increased from 4 mm. to 20-40 mm. Hg. From the cornpressor a conduit 4 conducts the compressed vapours to a condenser 5. Into this conduit 4 cold spray-water can be introduced as jets 28 through an inlet 27, whereby the compressed and superheated water-vapour is cooled to saturation. In the condenser the vapour and condensate are conducted through tubes. The condensate is withdrawn through a pipe 26 having a length h which is somewhat less than the length H of pipe 15, whilst uncondensed gases are withdrawn through an outlet 25. The condenser 5 is cooled by a mixture. of snow and water from a mixer 22. Through a pump 23 and a conduit 24 the mixture is conducted into the condenser around its tubes at a temperature of approximately 0 C. and withdrawn through an outlet 24 for being utilized for other cooling purposes if desired.

The evaporation vessel 1 can be equipped with observation glasses 29 and 30 at different levels. -Within the vessel there are inclined plates 13 for the distribution and spreading of the entering lye into thin layers so as to facilitate the evaporation. At the bottom 14 of the evaporation vessel there is an outlet 15 in the form of a vertical pipe having a length H which may be (approximately m. length) for concentrated lye and ice-crystals, collected in a collecting vessel 16, from where a pump 17 or the like pumps a part of the lye and smaller ice-crystals through a duct 18 back to the mixer 9 in order to be reintroduced into the vessel 1 together with new quantities of lye. The remaining portion of the concentrated lye from the vessel 16 and (bigger) ice-crystals are conveyed by a conveying device 19 to a separator 20, where concentrated lye is separated from ice-crystals, and in which a possible washing may take place. The separated ice can be used in the mixer 22 and/or in the cooler 7. The concentrated lye, called thick-lye, is discharged through an outlet 21.

The compressor 3 can be of any known kind. In this case two different types are very suitable, namely turbocompressor and vapour jet compressor.

For the condensation in the condenser 5, large quantities of cooling water are at disposal of a temperature as low as 0 C.-even cooling water mixed with snowwhich in both the aforesaid compressor-types highly faciliice-crystals can be separated from large ones.

tates condensation of the water-vapour. The cold water, that is to say the ice-water, is obtained'by melting of the snow, which remains after the separation of the thick lye from the snow in the separating device 20 (possibly also washing). Such ice-water is also obtained from tha second stage, whereby suicient cooling capacity is avail" able.

The evaporation vessel 1 should be such as to maintain the quantity of evaporated vapour small, approximately 5%, in relation to the quantity of lye, and to this purpose the volume of the escaping vapour, in spite of the modest pressure (approximately 4 mm. Hg), will not be particularly large. If the vapours (in spite of the low tempera ture) are slightly acid, the acid can he removed by known methods, before the vapours arrive at the compressor 3. The low pressure-approximately 4 mm. Hg=54 mm. water-column-requires that the lye is spread on the plates 13 in layers of only a few mm. thickness. The plates can be perforated with holes or slots, or uted. The lye with ice-crystals is allowed to iow from one plate to the other, suitably having increasing inclination, since the quantity of ice-crystals augments in direction downwards from plate to plate. The plates can also be shaped as spirals. The more the concentration of the lye increases, the more viscous will the lye become (see table II), whereby the mixture of lye and ice-crystals obtains the consistency of a thickly-ilowing liquor. The outlet 15 can therefore be made as a vertical pipe, but also a pump or any other known method can be applied. The ratio between the quantity of ice-crystals and lye is to be kept at rather low content of ice-crystals, for which reason the lye normally has to circulate several times. Moreover, the ice-crystals must be big, so as to facilitate the separation of lye from ice-crystals. This is achieved if the icecrystals will get time to grow, and it is therefore important that the mixture of lye and ice-crystals in the evaporation vessel 1 is allowed to pass during a suthcient period of time.

As aforesaid, when the lye is separated from the icecrystals in connection with the circulation of the lye, small The large crystals pass to the device 20, and the small crystals pass in circulation into the vessel 1 anew in order to grow further. The .growth of the crystals takes a long time, since for example a crystal of cubic form of linearly the double size contains- 8 times as much substance as the original one.

The cost for freezing-out ice at low pressure is reduced considerably if the temperature of the condenser 5 can be kept low, for example from 0 C. to +10" C.` This is possible if one has access to such large quantities of ice that al1 evaporated water (that is to say vapour from the compressor 3)-l-the vapour from the spray water at 28 (for eliminating the super-heating) as well as the heating vapour (vapour jets) can be condensed in the condenser at low temperature (for example from 0 C. to -l-l0 C.). In order to get this quantity of snow, it is necessary not only to use the snow, obtained in stage 1, but also the snow obtained in stage 2. These quantities of snow amount to the ratio 2:3 to 1:3 or possibly 3:4 to 1:4. The viscosity is then suitable, (see table Il) because at 5% to 6% evaporated liquid, the viscosity (at +15 C.) will be 4.57 and 6.85, respectively, and-calculated at the respective freezing-points-11.4 C. and 17.1 C., respectively. This is a good reason forA the division into two steps or stages, as suggested according to the invention.

The condenser 5 -is constructed slightly differently depending on whether a turbo-compressor or a vapour jet ejector be used. In the former case, direct or indirect cool# ing can be used; in the latter case there is almost always used direct cooling (mixing of cooling-water into the vapour). Further, in the condensation cooling can be eiected with water mixed with ice, whereby the very lowest temperature is obtained. In freezing of the sulphite lye the vapour j'et ejector with ice mixed water as direct cooling in the condenser is particularly recommended, because the freezing-point of the sulphite lye lie-s only a few degrees below C. and with ice-waterthe condenser can be maintained at only a few degrees above 0 C., whereby the entire range of compression can be kept so low as between C. and 10 C. This results in an inexpensive compression.

The thick-lye discharged from the first stage through the outlet 21 has, as mentioned above, such a great viscosity, that one cannot continue its concentration by evaporation at the freezing-point. The lye is viscous and the ice-crystals are small (at increasing concentration of the lye the ice-crystals grow more and more slowly). When freezing is continued one has to proceed more carefully and at least partly supercool the viscous lye. Such cooled lye has all'uviated ice-crystals in it, which grow further due to the super-cooling of the lye. The second step or stage of the process therefore aims at freezing under agitation.

As cooling-surfaces it is preferable to use tubes 40 (FIG. 2) having a diameter of approximately 50 to l00 mm. and for example arranged horizontally and cooled by a coolant (for example liquid ammonia) circulating in the tubes. These cooling-tubes are suitably placed above each other in a vertical plane (a vertically arranged coil). A plurality of such coils are arranged beside and at suitable distance from each other. The lye can be permitted to flow over the tubes, but it is preferred to mount the cooling-coils in troughs of wood, concrete or the like, filled with lye. However, the cooling-surface `rnust be kept clean from ice, for instance by means of annular Scrapers 67, which are reciprocated, sliding on' the outside of the tubes. The coolant can suitably be supplied to the cooling-coil at three points 45, 46 and 47. The surplus coolant can be collected at 48 and be returend to storage containers for coolant to a known manner.

-FIG. 3 shows how two tubes 40 and 41 can be connected with each other at the ends so as to prevent snowbarriers from being formed, which could hamper the scraping clean of the tubes. A lconnection 42 between the tubes 40 and 41 has a smaller diameter than the two tubes as best shown in FIG. 4. A heat insulating layer 43 (FIG. 4) is provided on the tube 42 in order thereby to prevent snow (ice)-forrnation on the surface of the tube. According tol FIG. 4 this insulation has a diameter which is 2 l.5=3 mm. smaller than the outer diameter of the cooling-tube, so that the scraper may pass over the heatinsulating part. In FIG. 4 it is assumed, that the scraper passes over approximately mm. of the insulated tube-part, but this is not necessary. If the tubes are 4000 mm. long, `the overall scraping-length will be 40004-20 +20=4040 mm. Since the connecting-pipe 42 between two tubes is thinner than the tubes 40, 41, there is formed (at horizontal arrangement) a space 44, which is lled with liquid coolant, whereby coolant will be present in all cooling-tubes. The surplus of coolant iiows over to the cooling-tube next underneath.

FIG. 5 shows a device for reciprocating the Scrapers 67. In the vessel 49 containing the cooling-tubes 40 there is a carriage 50 by theaid of which the Scrapers are reciprocated by means of special dogs or the like. The carriage 50 is supported by the dogs or the Scrapers and the latter are slidingly carried on the tubes. Since the sulphite lye is rather viscous (see Table II), it will serve as lubricant, when the Scrapers move on the coolingtubes.

The motion of the carriage and the Scrapers is achieved by means of ropes or chains, for example. FIG. 5 shows tour ropes 51, 52, 53 and S4. In order to operate the carriage there are required four additional ropes at the other end of the carriage (not shown in FIG. 5). The speed of motion can be l0 to 20 sec. per m. The ropes run over wheels 55, 56, 57, S8, 59, 60 rigidly mounted and further over wheels 61 and 62, which can be elevated and lowered in order to stretch the ropes. Such a stretching device is .shown at 63, 64 with load 65. The drivingshaft 66 is driven alternately forth and back in known manner. The adjustment of the stroke-length as well as of the correct placing of the scraping-length on the tubes is also carried out in known manner.

With increasing concentration of the sulphite lye the ice-crystals formed will tend to become smaller and smaller. By cautious scraping ice-crystals already formed floating in the lye can be caused to grow, namely if the lye is cooled so as to be slightly super-cooled. This is achieved if the cooling is effected very carefully.

The Scrapers 67 can consist of two ring-halves, which enclose the cooling-tube, and are held together by a bolt or similar such, that a small clearance exists between the tube and the scraper moving thereon. Each tube can have one scraper (but there can also be varranged a plurality of Scrapers) reciprocating by means of dogs 69, 70 (FIG. 4) or the like, preferably comprising flat irons, angle irons or similar, mounted on the carriage 50.

The scraping-effect will be improved if the points o-f engagement between the scraper-ring and its driving means are at some distance from the -outer diameter of the tube and preferably the points of engagement may take the shape of small abutments 71, 7.2. Thus, under the inliuence of the pressing force the ring will slant slightly against the tube, so that the ring will engage the tube with a sharp scraping edge 73. During the movement of the scraper in reversed direction, the pressing force will act upon the abutment 72 at the bottom of the ring and the sharp scraping edge will then be at 74.

The snow-crystals iioat up, towards the surface of the lye and there form together with the lye a heavy-flowing mass of paste-consistency. It can be withdrawn easily from the top part of the vessel, simply by lowering the overflow edge at the end walls of the vessel. The carriage 50 will displace the ice-crystals towards these end walls. Thereafter the lye is separated from the snowcrystals in known manner and the snow-crystals are washed with lye of lower concentration, and with water, respectively. The thick lye obtained, called the thickest lye, is withdrawn from the system and process-ed further into different products according to known methods. Washing liquid is introduced again into the vessel, possibly together with a part of the thickest lye.

In the second step or stage of the process, where the lye ultimately gets very thick-flowing, it is suitable to divide the freezing operation into two or a plurality of sub-stages with falling freezing-points. Hereby, the greatest lye-concentration can be achieved.

The less the difference between the evaporation-temperature and the condensation-temperature, the less power is required for the compression of the water-vapour. A very great technical eiect is therefore gained by dividing-according to the invention-the concentration of the lye into two stages while utilizing the ice (snow) from both these stages for cooling the condenser 5 in the first stage, whereby the temperature in this condenser can be kept so low as only some degrees above 0 C.

FIGURES 6 and 7 show two different alternativesof cooling of the condenser. In the construction of FIG. 6, which is employed when compressor 3 is a turbo-compressor, the condenser 5 has an inlet 32 for ice-water and a duct 33 from the turbo-compressor as well as a duct 34 for uncondensed gases from the condenser to the vacuum-pump. In the alternative construction according to FIG. 7, which shows a condenser 5" to be used with a vapour jet compressor 36, a mixer 31 is used for preparing snow-water-mixture and a duct 33a is connected to the vapour jet compressor 36 for passing both the evaporated water-vapour and the processing vapour into the condenser 5. Uncondensed gas is discharged through the duct 34a.

Kcal. per kg. of processing vapour Condensation temperature C):

The basic idea of the invention, namely division into two stages and utilization of snow from both these stages for cooling the condenser of the iirst stage, whereby the temperature of said condenser will be lowest possible, renders obviously a very great technical effect.

The entering sulphite lye from the sulphite cellulose mill can be cooled down by evaporation of water at low pressure (vacuum), or by indirect cooling in heat-exchangers by means of the large quantities of cold water, which depart from the condenser, or by indirect cooling in heat-exchangers by means of discharged thickest lye, having a temperature of approximately -4 C.

What I claim is:

1. A process to concentrate sulphite lye and similar lcomposite aqueous liquors by freezing, comprising steps of irst cooling the liquor to approximately 0 C., and then freezing it in at least two successive stages, the rst stage comprising partial evaporation of the water-contents of the liquor and freezing of ice under influence of vacuum approximately at the freezing-point of the liquor, the liquor thus concentrated being cooled in the second stage to temperature lower than this freezing-point, preferably approximately at atmospheric pressure, and conveying the ice crystals formed in the same direction -as and together with the mother lye.

2. A process according to claim 1, wherein ice prod-uced during the rst stage is partially separated from the liquor. p

3. A process according to claim 1, wherein part of the liquor and the ice from the first stage is circulated back to the input of the first stage.

4. A process according to claim 1, wherein said liquor in a vacuum-evaporator is passed over inclined surfaces permitting prolonged retention-time for the liquor in said evaporator, and comprising separating large ice crystals from small ice crystals, and returning the small ice crystals to the beginning of the first stage.

5. A process according to claim 1, wherein vapour from the evaporation is first compressed and subsequently condensed in a condenser.

6. A process according to claim 1, wherein the condensation is effected while utilizing ice obtained by freezing the liquor and cold water separated from said liquor.

7. A process according to claim 1, wherein the liquor is supercooled and the freezing in the second stage is effected while agi-tating the supercooled liquor and wherein the ice-crystals formed are separated from the liquor.

8. A process according to claim 7, wherein the liquor during the second stage is passed over cooling-surfaces, and the ice thus froozen-out from the liquor is scrapedoi from said cooling-surfaces by means of reciprocating scraping-means.

'References Cited by the Examiner UNITED STATES PATENTS 828,888 8/ 1906 Hoofnagle 62-58 2,780,281 2/1957 Reinert. 2,868,830 1/1958 Weedman 62-58 2,896,419 7/ 1959 Thompson 6'2-58 3,050,952 8/ 1962 Marwil 62-58 3,098,735 7/ 1963 Clark 62-58 3,103,792 9/1963 Davids 62-58 3,121,626 2/1964 Zarchin 62-58 FOREIGN PATENTS 985,905 3/1951 France.

NORMAN YUDKOFF, Primary Examiner.

G. HINES, Assistant Examiner. 

1. A PROCESS TO CONCENTRATE SULPHITE LYE AND SIMILAR COMPOSITE AQUEOUS LIQUORS BY FREEZING, COMPRISING STEPS OF FIRST COOLING THE LIQUOR TO APPROXIMATELY 0*C., AND THEN FREEZING IT IN AT LEAST TWO SUCCESSIVE STAGES, THE FIRST STAGE COMPRISING PARTIAL EVAPORATION OF THE WATER-CONTENTS OF THE LIQUOR AND FREEZING OF ICE UNDER INFLUENCE OF VACUUM APPROXIMATELY AT THE FREEZING-POINT OF THE LIQUOR, THE LIQUOR THUS CONCENTRATED BEING COOLED IN THE SECOND 